The present invention concerns a vibration-insulating bearing arrangement for a drive unit and, more particularly for an engine, e.g., an internal combustion engine, by itself or in combination with a transmission.
It is known that such a bearing arrangement must absorb forces resulting from the mass of the drive unit, i.e., due to the weight of the unit as well as acceleration and deceleration forces, and from torques dues to the reaction moment produced by the output shaft of the drive unit and possibly moments generated by the mass related forces. It is known from German Letters of Disclosure 26 15 503 that it is difficult to design the known type of bearing arrangments for drive units in automobiles in such a manner that the desired vibration suppression, i.e., the prevention of the transmission of noises into the automobile proper, is ensured for the various stresses, both forces and torques. The design of such units is made even more difficult in that the mounting or suspension must respond to two opposite requirements. On the one hand, in order to reduce as much as possible the transmission of vibrations into the supporting framework, and thereby into the vehicle proper, i.e., in order to diminish the transmission of vibrations of the drive unit into the vehicle, the bearings in the bearing arrangement must be yielding. On the other hand, however, for reason of travel and driving dynamics, the relative movements between the drive unit and the vehicle proper ought to be small. This, in turn, necessitates a relatively unyielding design for the individual bearings of the bearing arrangement. A method is known, however, whereby these two opposing aspects are taken into account by the use of bearings with progressive spring characteristics, i.e., bearings which have a relatively hard effect only at larger vibration amplitudes. However, in the final analysis, such bearings are also unsatisfactory in that the static or quasi-static bearing loads vary within a relatively wide range and may push the working point of the bearing into the progressively stiffer spring zone even for small vibrations.
The aforementioned German Letters of Disclosure No. 26 15 503 describes a bearing arrangement that provides individual bearings for the internal forces that occur in the various coordinate directions, so that ideally the design of each individual bearing can be effected optimally in consideration of the inertial forces that occur in the associated coordinate direction. Two webs or bars are provided in this design for torque bracing of the drive unit. When the axis of one of the bars passes through the torque axis containing the center of gravity of the drive unit, the other bar need not absorb any inertial forces, i.e., it can be dimensioned in consideration of its purpose as a torque bracing. However, as in the past, this one bar is subject to double the stress due to the torques and inertial forces which occur. Moreover, it has been found that the vibration paths, which are contingent upon the manner of operation of the engine, when viewed from the vector point of view, may extend within an ellipse, whereby the individual vibration insulation in the direction of the individual bars may be disturbed because the vibration is no longer in the direction of the bars.